Simloop — Simloop

A general-purpose discrete event simulation (DES) framework for Node.js, written in TypeScript.

Simloop provides a minimal, type-safe API for building simulations of real-world systems. You define events, entities, and handlers — the framework runs the event loop.

Why Simloop?

Type-safe — generic TEventMap gives full autocomplete and type checking on event scheduling and handling
Zero runtime dependencies — only Node.js built-ins
Deterministic — seeded PRNG ensures reproducible results
Simple API — define handlers with sim.on(), schedule events with ctx.schedule()
Built-in statistics — online mean, variance, min, max, count
Pluggable logging — bring your own logger or use the default console logger
Dual module format — ESM and CJS

Quick Start


npm install simloop


import { SimulationEngine } from 'simloop';
 
// 1. Define your event types
type Events = {
  'customer:arrive': { customerId: string };
  'customer:serve': { customerId: string };
};
 
// 2. Create the engine
const sim = new SimulationEngine<Events>({ seed: 42, maxTime: 100 });
 
// 3. Register handlers
sim.on('customer:arrive', (event, ctx) => {
  ctx.stats.increment('arrivals');
 
  ctx.schedule('customer:serve', ctx.clock + 2, {
    customerId: event.payload.customerId,
  });
 
  const nextArrival = ctx.dist.exponential(0.2)();
  ctx.schedule('customer:arrive', ctx.clock + nextArrival, {
    customerId: `C${ctx.stats.get('arrivals').count + 1}`,
  });
});
 
sim.on('customer:serve', (event, ctx) => {
  ctx.stats.increment('served');
});
 
// 4. Initialize and run
sim.init((ctx) => {
  ctx.schedule('customer:arrive', 0, { customerId: 'C1' });
});
 
const result = sim.run();
console.log(result.stats);